Electromechanical transducer



y 1953 J. ANDERSON ETAL 2,645,683

ELECTROMECl-IANICAL TRANSDUCER Filed Dec. 17, 1949 3 1431/! J/ vaz'g' ol ,PaJAerKDMM Y (Ittomeg with the crystal.

Patented July 14, 1953 UNITED STATES PATENT OFFICE ELECTROMECHANICALTRANSDUCER Leslie J. Anderson, Moorestown, N. J and Robert K. Duncan,Woodburn, Ind., assignors to Radio Corporation of America, a corporationof Delaware Application December 17, 1949, Serial No. 133,572

14 Claims.

This invention relates generally to electromechanical transducers, andparticularly relates to a transducer having a movable vibratile elementand a fixed transducing element.

As is well known, a semi-conductor amplifier may consist of asemi-conducting crystal such as, for example, a germanium crystal'havinga with the crystal and usually consist of wires The base electrode isusually a response to acoustical signal variations in a predeterminedmanner, thereby to derive an output current which varies in accordancewith the accoustical signal.

An electro-mechanical transducer in accordance with the presentinvention comprises a semi-conductor device provided with a base elec:-trode, an emitter electrode and a collector electrode and wherein thedistance between the emitter and collector electrodes is varied by thevibratile movement of. an element which'may be the diaphragm of amicrophone or the stylus of a phonograph pick-up device, the elementbeing having a pointed end in contact with the crystal. It is well knownthat the current or voltage gain of such a semi-conductor amplifier is afunction of the distance between the emitter and collector electrodes.Thus, the gain increases when the distance between the two rectifyingelectrodes decreases. Consequently, the outputcurrent becomes greater asthe distance betweenthe emitter and collector electrodes decreases.

In accordance with the present invention, the distance between theemitter and collector electrodes is varied in response to an externalvibratory force applied thereto mechanically in such a manner as toobtain a high signal output. Thus, by way of example, the distancebetween the two rectifying electrodes, that is, the emitter andcollector electrodes of a semi-conductor amplifier may be varied by thestylus of a phonograph pick-up or by the diaphragm of a microphone inorder to obtain an electro-mechanical transducer.

It is accordingly an object of the present invention to provide a novelelectro-mechanical transducer having a semi-conductor device as thetransducing element thereof.

A further object of the invention is to provide a mechanically modulatedsemi-conductor amplifier wherein the distance between the emitter andcollector electrodes may be varied at any desired rate to vary the gainand to produce an output signal, as by the vibratile movement of anelement such as the stylus of a phonograph pick-up device or thediaphragm of a microphone. l

Another object of the invention is to provide a novel electro-mechanicaltransducer including a germanium crystal'provided with a base electrode,an emitter electrode and a collector electrode and means for varying thedistance between the emitter and collectorelectrodes in carried by orconnected with one of the elec-,

trodes of the device;

In a present preferred form of the invention, the germanium crystal is.vibrated with respect to the emitter and collector electrodeswhich arein contact with inclined surfaces of the crystal. The two electrodes areprovided with smooth tips and are mounted and arranged in such a mannerthat thetips roll or, rock over the inclined contact surfaces when thecrystal is vibrated by the vibratile element. With this arrangement, ithas been found that the output current derived from the amplifier iseffectively varied in accordance with an applied acoustical signal andmay be further amplified before being reproduced.

The novel features that are considered characteristic of this inventionare set. forth with particularity in the appended claims. ventionitself, however, both as to its organization and method of operation, aswell asgadditional objects and advantages thereof, will best beunderstood from the following descriptionment and its electrodes takenin the direction of the arrow of Figure 3; and r Figure 7 is a schematiccircuit diagram showing the transducer of the present invention cou:

.pled to an audio frequency amplifier and; a loud speaker.

Referring now to the drawing in which like The in conventional manner.

trode I3.

reference numerals throughout the'figures, and particularly to Figure 1,there is illustrated a transducer in accordance with the inventioncomprising a semi-conductor device. The semiconductor device includesbody IQ of semi-conducting material which mayconsist, for example, ofboron, silicon, germanium, 'tellurium or selenium containing a small butsufficient number of atomic impurity centers or lattice imperfections ascommonly employed for best results in crystal rectifiers. Germanium isthe preferred material for body It and maybe prepared so as 'to be anelectronic Ntype semi-conductor as is well known. The surface ofsemi-conducting body It may be polished and etched 'in a It is. alsofeasible to utilize a germanium block from a commercialhighbacl-:-voltage germanium rectifier such as the type 1N34 in whichcase further surface treatment may not be required.

Semi-conducting body III is provided with emitter electrode I I,collector electrode I2 and base electrode I3. Emitter electrod II andcollector electrode I2 are usually small area electrodes and may bepoint contacts consisting, for example of tungsten or Phosphor bronzeWires having a diameter of the order of 2-to 5 mils. The two electrodesII and I2 are normally spaced approximately two mils apart. Emitterelectrode IIand collector electrode I2 make rectifying, high resistancecontacts with body III. Since electrodes I'I'and I 2 are normallypressed against body 59' Without being welded or otherwise fixed to bodyon body It and hence is in fixed contact there- "with.

A comparatively large reverse bias voltage is normally impressed betweencollector electrode I2 and base electrod I3. If it is assumed that bodyI0. consists of an N type crystal which is believed to have a P typesurface layer, a negative potential should be impressed on collectorelectrode I2. To thisend there may beprcvided battery I5. havingitspositiveterminal grounded while its negative terminal is connected tocollector electrode I2 through load resistor I6. Base electrode I3 mayalso be grounded as shown. A comparatively small forward bias voltage isprovided between emitter electrode I I and base elec- Assuming againthat body I0 consists of an N type crystal which is believed to have a Ptype surface layer, a positive potential should be impressed on emitterelectrode'l I. To this end there is provided biasbattery I'I having itsnegative terminal grounded While its positive terminal is connectedthrough resistor I8 to emitter electrode II. The purpose of resistor I8is to limit the currentwhich is allowed to flow through emitterelectrode II. It may be pointed out that the required bias potentialbetween emitter electrode I I and base electrode I3 may also be providedby a bias network as is conventional.

An output signal may be derived from output terminals 20, one of whichis grounded while the other one is coupled to collector electrode I?through coupling capacitor 2I. The circuitof Figure l as describedherein will develop a corn stant current flowing through load resistorIt so that no signal is developed at output terminals 20.

In accordance with theflp'resentinvention one of the electrodes I I 01"I2 is mechanically vibrated with respect to the other electrode. As willbe pointed out hereinafter in connection with Figure 2 it is also.teasible to vibrate body II] or base electrode I3' which is fixedthereto, with respect to v electrodes II andI2.

Thus, a mechanically vib-ratile element such as the stylus of a phonograph pick -up device or the diaphragm of a microphone may be connected,for example, to emitter electrod I I to rock it over the surface ofsemi-conducting body IQ as indicated by arrow 22. Preferably, the tip ofemitter electrode II as Well as that of collector electrode I2 isrounded as clearl shown in Figure 1 to facilitate the rocking oroscillating motion of one of the electrodes with respect to the other. 7

Since the current flowing through load resistor I6 is a function of thedistance between electrodes II and I2 an output signal will be derivedacross load resistor It which may be obtained fromoutput terminals 2!).This output signal varies with the distance between emitter electrode IIand collector electrode I2 Whichin turn is controlled by thevibratileeleinent connected thereto.

It is also feasibleto control the amplification of a device as. shown-inFigure 1. If an input; signal is'impressed across resistor I8, the am-.

plitude of the outputsignal derived from terminals:

20 may be varied" by rocking, for example, elec-. trode I2. This may beaccomplished manually orby an electromagnetic solenoid attached to elec.trode I2. Thus, the gain of the amplifier illmay be controlledinaccordance with a signalsuch as; an AVC voltage. Y

A preferred embodiment of the present inyen tion islillustrated inFigured. Although Figure,

2 shows a phonograph pick-updevice embodying;

the present invention it is to be understood that; the principles of theinvention are also applicable to a transducer including a microphone. Inthe; phonograph pick-up device of Figure 2 a phone-- graph stylus M isconnected mechanically to, crystal III; thereby to vibrate it withrespect to its; emitter and collector electrodes II, I2. For this;

purpose, crystal I6 is of wedge shape and'has two;

inclined surfaces 24 and 259s shown more clear-. .ly in Figures 3 to 6.Inclined surfaces 25, 25 may form an angle of 90. degrees or less.Surfaces 24', 25 are lapped, polished and acid etched as isconventional. v

Emitter electrode II and collector electrode I2 consist of wires of athickness of approximately twomils having loop shape intermediateportions as shown particularly in Figure 6 to provide a spring action.The free ends of emitter andcollectorelectrodes II and I2 are solderedor otherwise secured to metallicrods 26, 2-? which may be Rods 2'3, 21-extend through blocl:

.the direction of 'arrow 50 in Figure 3.

sition of surfaces 24, 25 of crystal l may be ad- J'usted by rotation ofscrew 35 which may be locked by lock nut 31.

Upright arm 36 is securedto or integral with hollow shaft 38 having adownwardly extending sleeve4|l for receiving a -phonograph stylus 4|.Stylus 4| is held by screw 42 having a knurled head 43, the screwcooperating with an internal thread in shaft 38. Shaft 38 is mounted intwo bearings formed by an upper plate 44 44 and a corresponding openingis provided in spring plate 45 as well as in a lower or base plate 50.

Stylus 4| and crystal ID are normally maintained in a center position bycentering spring 5|. As clearly shown in Figure 2, centering spring 5|consists of a stiff flexible wire secured between shaft 38 and bracket52 which is fastened by screws 53 to upper plate 44.

into their normal center position. A further damping means may beprovided comprising a plate 54 which may consist of Viscaloid or anyother suitable damping material and which is rigidly secured to shaft38. The upper end of plate 54 may be secured by bracket 55 to anup-right 56 integral with or fastened to upper plate 44.

When the pickup device of Figure 2 rides over a record, stylus 4| ismechanically vibrated in the direction indicated by arrow 58. This willvibrate crystal [0 about its pivot which is represented by the axis ofshaft 38. It will be noted that stylus 4|, shaft 38 and electrodes I2are arranged substantially in a plane to prevent. slippage of theelectrodes. Stylus 4| is forced to. vibrate against the action of spring5| and mechanical damping is provided by rubber sleeves 45, 41 and bythe Viscaloid plate 54. The relative movements of emitter and collectorelectrodes II and I2 with respect to crystal Ill are shown more clearlyin Figures 3 to 5. Thus, Figure 4 illustrates the normal or centerposition which crystal l8 assumes with respect 5 to electrodes and I2under the influence of spring, 5|. The distance between electrodes and 2in this position may amount, for example, to three mils. The stylus isdiagrammatically represented at 4| and the. pivotal axis at 38. Let

it now be assumed that stylus 4| is'moved in Accordingly, crystal |flmoves toward the right and the distance between emitter and collectorelectrodes H, l2 may be reduced, for example, to

one mil. Electrodes |2 are pressed into contact with crystal surfaces24, 25 by the spring action of their intermediate loops. If stylus 4|moves in the direction of arrow 6| (Figure 5), crystal It will move tothe left. the distance between electrodes ll, I2 now increases and mayamount, for example, to 5 mils.

It is to be understood that crystal I!) may also be vibrated byconnecting it to the diaphragm" of a microphone instead of connecting itto a 70 phonograph stylus. The loop shape intermediate portion ofelectrodes H and 12 are clearly shown in Figure 6. The electrodes shouldbe shaped in such a manner that they assert substantiallyhequal pressureon body [0 in their 75 Crystal l0 and stylus 4| ex- 16 Spring 25 5| alsotends to return stylus 4| a nd crystal Consequently, as

6. various operating portions shown in Figures 3 to 5. 'The tips ofelectrodes H and I2 are rounded as clearly illustrated in Figures 3 to 5to facilitate their rocking motion across surfaces 24 and 25.

Preferably, the transducer of the invention is prepared by pulsingelectrodes II and 2 with an electric current of short duration afterthey have been assembled. Usually, it is only necessary to discharge,for example, a capacitor between collector electrode 2 and baseelectrode l3. In accordance with the present invention, this ispreferably effected by pulsing the collector electrode |2 while stylus4| rides on a record having recorded thereon with maximum amplitude a500 or 1,000 cycle standard tone. In this. manner the entire surface 25over which collector electrode |2 rides during the normal op-- erationof the transducer of the invention will. be electrically treated. 7

As pointed out hereinbefore, connection may be made to electrodes l2through lugs 32: and 33. Connection to the base electrode l3 or screw 35may be made through bracket 52 which is electrically connected to screw35 by spring 5|, shaft 38 and arm 36. Figure 7 illustrates by way ofexample a circuit diagram of the transducer of the invention connectedto a vacuum tube audio frequency amplifier 66 and a loud. speakerl5.Semi-conducting body I0 is again provided with base electrode l3 andwith emitter electrode H and collector electrode 2. Arrow 62 indicatesthat crystal l0 may be mechanically; vibrated as explained hereinabove.Base elec-- trode I3 is grounded as shown while collector electrode I2is connected to the negative terminal of battery |5 through loadresistor l6. Emitter battery has its negative terminal grounded.Potentiometer resistor 53 is connected across battery l1 and apredetermined. voltage may be obtained from variable tap 64 connected toemitter electrode through resistor I8.

In accordance with the above explanation a voltage is developed acrossload resistor l6 which varies with the distance between electrodes I andI2. This output voltage is coupled through capacitor 2| to control grid65 of audio amplifier 69 which may be a pentode as shown. The cathode ofaudio amplifier '69 may be grounded as shown while the control grid 65is grounded through grid leak resistor 66 connected to grid bias battery61. The anode voltage supply is indicated by battery i0 connected'to theplate of amplifier 69 through inductor H. The screen grid of amplifier66 is connected to battery 70 through dropping resistor 12 bypassed toground by capacitor 13.

The audio signal is thus amplified by amplifier 59 and is impressed oninductor 14 which is magnetically coupled to inductor II and is thenreproduced by loudspeaker 75.

It is to be understood that amplification of the output signal derivedfrom the transducer of the invention may not be necessary particularlyif the audio signal is reproduced by headphones.

There has thus been disclosed a novel semiconductor transducer embodyinga semi-conductor device of the transistor type. The output signal is afunction of the distance between the emitter and collector electrodeswhich is varied by a vibratile' element such as the stylus of'aphonograph pickup or the diaphragm of. a microphone. i

body to a normal centered position with respect to said emitter andcollector electrodes.

10. An electro-mechanical transducer comprising a semi-conducting bodyhaving two angularly disposed surfaces, a base electrode in fixedcontact with said body, emitter and collector electrodes, eachconsisting of a filamentary conductor, a support having secured theretoone extremity of each of said conductors, the other extremity of each ofsaid conductors having means whereby they are in movable contact withone of said surfaces, each conductor having a resilient loopshapedintermediate portion for pressing said emitter and collector electrodesagainst said surfaces, means for pivotally supporting said body fromsaid support, a movable stylus element having means whereby it ismechanically secured to said body and adapted to vibrate said body aboutits pivot, thereby to move said body with respect to said emitter andcollector electrodes and to vary the distance between said emitter andcollector electrodes, a spring secured between said body and saidsupport for urging said body and stylus element into .a predeterminedposition, and means connected between said body and said support fordamping the vibrations of said body and stylus element.

11. An electro-mechanical transducer comprising a semi-conducting bodyhaving at least two surfaces angularly disposed with respect to eachother, a base electrode in fixed contact with said body, emitter andcollector electrodes, each consisting of a fine wire, a support havingsecured thereto one extremity of each of said wires, the other extremityof each of said wires having means whereby they are in movable contactwith one of said angularly disposed surfaces, each wirehaving aresilient loop-shaped intermediate portion, means for pivotallysupporting said body from said support, a phonograph stylus having meanswhereby it is mechanically secured to said base electrode and adapted tovibrate said body about its pivot, thereby to move said body withrespect to said emitter and collector electrodes and to vary thedistance between said emitter and collector electrodes, a springconnected between said base elecrtode and said support urging said bodyand stylus into a normal position, and means provided between said baseelectrode and said support for damping the vibrations of said body andstylus.

12. An electro-mechanical transducer comprising a support, asemi-conducting body having two adjacent surfaces angularly disposedwith respect to each other, said body having means whereby it ispivotally carried by said support and capable of vibrating about apredetermined carried by said support, the other end of each conductorhaving means whereby it is in contween said body and said support forbiasing said them against their respective surfaces, whereby thedistance between said conductors varies in response to vibratilemovement of said body, and a spring secured between said body and saidsupport for resiliently holding said body in a predetermined position. l

13. An electro-mechanical transducer comprising a support, asemi-conducting body having two adjacent surfaces angularly disposedwith respect to each other, said body having means whereby it ispivotally carried by said support and capable of vibrating about apredetermined pivotal axis, said adjacent surfaces having means wherebythey are disposed with respect to said pivotal axis so that their apexis capable of V vibrating in an arc about said pivotal axis, two

tact with an individual one of said adjacent.

flexible thin wires, means whereby one end of each wire is carried bysaid support, the other end of each wire having a rounded tip in contactwith an individual one of said adjacent surfaces, said wires having eacha resilient loopshape intermediate portion for urging them against theirsurfaces, whereby the distance between said tips varies in response tovibratile movement of said body, and a spring secured between said bodyand said support for resiliently holding said body in a predeterminedposition.

14. An electromechanical transducer comprising a support, asemi-conducting body having two adjacent surfaces angularly disposedwith respect to each other, a large-area electrode in fixed contact withsaid body, saidbody having means whereby it is pivotally carried by saidsupport and capable of vibrating about a predetermined pivotal axis,said adjacent surfaces being disposed with respect to said pivotal axisso that their apex is capable of vibrating along a circle about saidpivotal axis, two thin wires, means whereby one end of each wire iscarried by said support, the other end of each wire having a smoothrounded tip in contact with an individual one of said adjacent surfaces,said wires having each a resilient loop-shape intermediate portion forpressing said tips against their associated surfaces, whereby thedistance between said wires varies in response to vibratile movement ofsaid body, a spring secured between said electrode and said support fornormally urging said body into a predeterminedposition and for biasingit against said vibratile movement, and means provided between saidelectrode and said support for dampingsaid vibratile movement.

LESLIE J. ANDERSON. ROBERT K. DUNCAN.

References Cited in the file of this patent UNITED STATES PATENTSWallace Apr. 17, 1951

